Techniques for evaluating the adhesion of a coating applied to a substrate include various test methods represented by, for example, JIS “K-5400.” According to the JIS “K-5400” method, incisions are made in a coating on a test piece, wherein the incisions penetrate the coating to reach a substrate of the test piece. Based on the extended damages of the coating at the incisions, vulnerability and/or adhesion to the substrate for the coating are determined. Also, if necessary, the adhesive cellophane tape peel test is conducted using the technique specified by JIS “Z-1552” for the coating damages created as above to thereby quantify the adhesion.
Traditional cross-cut methods generally involve making a predetermined number of incisions according to a specific test method being employed through the coating film being tested using a utility knife and a cross cutting guide, subsequently turning the cross cutting guide by 90° and then, making another predetermined number of incisions along the guide so that the incisions are made in a right angle lattice pattern (e.g., see Patent Document 1).
In such a cross-cut method using the cross cutting guide, the blades need to be frequently exchanged. This is because the tip of the utility knife is prone to be damaged by frequently contacting with the cross cutting guide with a very narrow slits. Also, the cutting work has been extremely tedious in order to avoid making mistakes such as cutting the same location two or more times, and failing to make incisions where needed, thus there is a need to improve the cutting work.
Responding to the above problems, there have been proposed coating film cutting tools capable of making a plurality of incisions simultaneously using a plurality of cutting blades positioned with a predetermined interval in the blade thickness direction (e.g., Patent Documents 2-4). When making incisions simultaneously using such plurality of blades, it is very difficult to make those incisions while uniformly maintaining the biasing force of each blade against the coating film. In particular, for coatings with the film thickness less than 20 μm, making accurate evaluations have been difficult due to an insufficient or excessive incision depth.
As one method for solving such problems, the present inventor proposed a method for making a plurality of incisions simultaneously by utilizing the attractive force of a magnet provided on the side of the substrate opposite from the side of the coating film to thereby pull the plurality of blades towards their cutting edge and maintain the blade tips in contact with the coating film, and moving the contact point relative to the coating film while the blade tips are biased against the film (Patent Document 5). Since the attractive force of the magnet acts on all of the plurality of the blades, each of the blades may move independently in the blade width direction (up or down direction) to maintain the contact with the coating film along the shape of the film, allowing the blades to stably make a plurality of incisions even through coating films with 10 μm or less thickness.